1. Field of the Invention
The invention relates to the production of catalysts, and specifically to a process for activating catalysts comprising as an active ingredient at least one of the following metals: copper, chromium, nickel, cobalt, manganese, zinc and aluminum.
Catalysts based on compounds such as oxides or salts of the above metals, in an active state are commonly used in methanol synthesis, conversion of carbon monoxide, hydrogenation of organic compounds and other catalytic processes of organic synthesis.
2. Description of the Prior Art
One widely used process for activating catalysts comprises reducing the metallic compounds contained therein to the metallic state or to compounds with a lower degree of oxidation, whereby the inactive form of a catalyst is rendered active.
The catalyst that is to be activated is usually in the form of pellets. The process of activation is generally carried out in container-type apparatus periodically charged with the catalyst mass in volumetric quantities, each equal to the volume capacity of the apparatus. In the process of activation, due to reduction of metals, the catalyst volume within the convertor becomes 10 to 20% less than the initial volume.
Known in the art is a process for obtaining a zinc-copper catalyst, which comprises reduction of the ZnO/CuO mass by passing therethrough a stream of gas consisting of hydrogen and a gas or gas mixture inert to the catalyst. The mixture of hydrogen reducing gas and an inert gas is passed through the catalyst until exit gases and inlet gases have approximately the same hydrogen content. The reduction temperature is maintained below 343.degree. C. by varying hydrogen content in the stream of gas. The hydrogen content is maintained to be less than 5% by volume and in the course of treatment of the zinc-copper mass, this content is increased within the range of 0.3 to 5% by volume (British Patent No. 1,082,298).
There is also known a process for reducing a ZnO-CuO catalyst, comprising passing through the initial catalyst mass a gas mixture based on a gas inert to the catalyst with an admixture of hydrogen and carbon monoxide sufficient for an exothermic reaction to proceed.
The concentration of the reducing ingredients mentioned above in the gas mixture is therewith gradually increased from 0.5 to 5% by volume. The process is carried out at a temperature ranging from 149.degree. to 288.degree. C. (British Patent No. 1,137,357).
Also known in the art is a process for activating a catalyst useful in converting carbon monoxide and consisting of ZnO and CuO precursors, the process being carried out at a temperature below 371.degree. C. In this process, the oxides forming part of the catalyst mass are acted upon by a gas stream comprising hydrogen as a reducing gas and a diluent gas selected from the group consisting of nitrogen, methane, ethane, propane or carbon dioxide. Reduction is effected with incremental increase in the reducing gas content in the gas stream. The temperature of the reduction zone is maintained in the range of 149.degree. to 260.degree. C. (British Patent No. 1,220,860).
Copper oxide-zinc oxide catalysts for use in low temperature carbon monoxide conversion processes are also activated by reducing the oxides in a gaseous medium comprising from 0.1 to 3% by volume of a reducing gas selected from the group consisting of hydrogen, carbon monoxide, and a diluent gas being the balance. The process is carried out at a temperature of 120.degree. to 177.degree. C. (U.S. Pat. No. 3,390,102).
There is known a process for reducing a Zn-Cu-Al catalyst useful in methanol synthesis by contacting the catalyst with a stream of a gas mixture constituted by hydrogen as a reducing gas and an inert diluent, such as natural gas or methane. The reduction process is carried out at standard or increased pressure and a temperature of from 120.degree. to 180.degree. C. (USSR Inventor's Certificate No. 403,427).
The reduction of copper catalysts used in methanol synthesis is taught in another prior art process as being carried out with a reducing mixture comprising a reducing gas, such as hydrogen or carbon monoxide in an amount of up to 10% by volume, carbon dioxide up to 15 vol % per volume of the reducing as, the balance being an inert diluent, such as methane, nitrogen. The reduction is effected at a temperature of 90.degree. to 130.degree. C. (USSR Inventor's Certificate No. 429,837).
As can be seen from the above analysis of the prior art, the activation of catalysts by reducing metal oxides constituting the catalyst mass is effected at a low concentration of a reducing gas in a gaseous mixture fed to the reaction zone, said concentration not exceeding the total volume of the gas being recycled. Such limitation is dictated by the hazard of catalyst particles sintering into a dense mass under the influence of heat from exothermic reduction reactions, and precludes the possibility of the activation process being thermally intensified and necessitates the temperature be confined to at most 280.degree. C.
In addition, the prior art processes for activating catalysts require considerable power inputs for heating and circulating the mixture of the reducing gas and the diluent gas. Thus, in the process disclosed in USSR Inventor's Certificate No. 403,427 the power inputs are 10,000 to 15,000 kW/h per ton of the catalyst mass.
It should also be noted that complicated equipment is required for the process for reducing catalysts with a mixture of reducing and inert gases, the volumetric ratio of which is to vary as the process cycle proceeds. Thus, for compressing a mixture of reducing and inert gases and for feeding it to a recycle system, a compressor must operate in combination with a ratio controller for said gases and be provided with a control circuit for taking account of variations in the physical and mechanical properties of mixtures of said gases in the case of different volumetric ratios thereof. A cumbersome drying system for drying large volumes of the circulating gas, also adds to the complexity of the equipment used to carry out the prior art processes. This drying system is a prerequisite for practicing the prior art processes, since feeding of an insufficiently dried circulating gas to the inlet of the activation apparatus lowers the rate of the process of reducing metal oxides and affects to a certain extent the quality of the catalyst thus activated.